System for transient voltage suppressors

ABSTRACT

A method of forming a silicon carbide transient voltage suppressor (TVS) assembly and a system for a transient voltage suppressor (TVS) assembly are provided. The TVS assembly includes a semiconductor die in a mesa structure that includes a first layer of a first wide band gap semiconductor having a conductivity of a first polarity, a second layer of the first or a second wide band gap semiconductor having a conductivity of a second polarity coupled in electrical contact with the first layer wherein the second polarity is different than the first polarity. The TVS assembly also includes a third layer of the first, the second, or a third wide band gap semiconductor having a conductivity of the first polarity coupled in electrical contact with the second layer. The layer having a conductivity of the second polarity is lightly doped relative to the layers having a conductivity of the first polarity.

BACKGROUND

The disclosure relates generally to high temperature semiconductordevices, and more specifically, to semiconductor devices for transientvoltage suppression in high temperature environments.

Although silicon devices have been used for preventing sensitiveelectronics coupled in parallel to the TVS device from being subjectedto voltage spikes caused by, for example, lightning strikes and beingdamaged, they are not suitable for high temperature operation. Silicondevices tend to leak higher current as temperature increases, with thecurrent reaching unacceptably high values in ambient temperaturesgreater than approximately 150° C., which makes them unsuitable to beused in ambient temperatures of 225° C. or more needed for aviationapplications requiring core engine-mounted electronics such asdistributed engine control. Moreover, known TVS devices typically arepackaged using epoxy encapsulation. Epoxy packaging tends to inducelarge thermal strains within the TVS device structure aboveapproximately 185° C. and to begin to decompose.

Turbine engine instrumentation for both aviation and power generationapplications often require expensive cooling, or moving the electronicsfurther away from the sensors and actuators resulting in increasedinstallation and wiring complexity and reduced sensor performance due tonoise. The electronics used in distributed controls in the aircraft aresubject to damage from voltage surges caused by lightning strikes andelectromagnetic interference (EMI). At least some known applications usetransient voltage suppression (TVS) devices, which may include featuressimilar to a Zener diode. Commercially available TVS devices made ofsilicon are unable to be used to protect distributed electronics placedclose to the engine core due to the high ambient temperatures they wouldbe exposed to.

BRIEF DESCRIPTION

In one embodiment, a transient voltage suppressor (TVS) assemblyincludes a semiconductor die in a mesa structure that includes asubstrate including a layer of a first wide band gap semiconductorhaving a conductivity of a first polarity, a second layer of the firstor a second wide band gap semiconductor having a conductivity of asecond polarity coupled in electrical contact with the substrate, thesecond polarity being different than the first polarity, and a thirdlayer of the first, the second, or a third wide band gap semiconductorhaving a conductivity of the first polarity coupled in electricalcontact with the second layer. The layer having a conductivity of thesecond polarity is lightly doped relative to the layers having aconductivity of the first polarity. The TVS assembly also includes afirst electrode coupled in electrical contact with the substrate and asecond electrode coupled in electrical contact with the third layer.When a voltage greater than a predetermined magnitude is applied acrossthe first and second electrodes, the TVS assembly operates in apunch-though mode that permits a relatively large amount of current toflow through the TVS assembly.

In another embodiment, a method of forming a silicon carbide transientvoltage suppressor (TVS) assembly includes providing a punch-throughsilicon carbide semiconductor transient voltage suppressor die thatincludes a first side and an opposite second side, encapsulating the diein a glass housing at least partially surrounding the die, and couplinga respective electrode in electrical communication with each of thefirst and the second sides, each electrode having a coefficient ofthermal expansion that substantially matches a coefficient of thermalexpansion of the glass housing.

In yet another embodiment, a high temperature electronic systemincluding an electronics unit configured for exposure to an environmenthaving a temperature greater than approximately 150.0° C., the remoteelectronics unit including a transient voltage suppressor (TVS) assemblycoupled in operative relationship with at least some electroniccomponents of the electronics unit, the TVS including a punch-throughsilicon carbide semiconductor TVS die encapsulated in a glass housing atleast partially surrounding the die, and coupled to electrodes using atleast one of a thermocompression bond, a transient liquid phase solderbond, a diffusion bond, and an alloyed layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presenttechnique will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic block diagram of an architecture of a power andcommunication distribution system in accordance with an exemplaryembodiment of the present invention;

FIG. 2 is a schematic block diagram of an exemplary one of theelectronics units shown in FIG. 1 in accordance with an exemplaryembodiment of the present system;

FIGS. 3A-3C are schematic block diagrams of various configurations ofvoltage suppression protection available using TVS 218 in accordancewith an exemplary embodiment of the present invention.

FIG. 4 is a side elevation view of a semiconductor die portion of atransient voltage suppression (TVS) assembly shown in FIG. 2 inaccordance with an exemplary embodiment of the present system;

FIG. 5 is a side elevation view of the semiconductor die portion of thetransient voltage suppression (TVS) assembly shown in FIG. 2 inaccordance with another embodiment of the present system;

FIG. 6 is a side elevation view of the semiconductor die portion of thetransient voltage suppression (TVS) assembly shown in FIG. 2 inaccordance with another embodiment of the present system;

FIG. 7 is a side view of the transient voltage suppression (TVS)assembly shown in FIG. 2 in accordance with an exemplary embodiment ofthe present invention;

FIG. 8 is another view of the transient voltage suppression (TVS)assembly shown in FIG. 2 in accordance with an exemplary embodiment ofthe present system;

FIG. 9 is a graph 800 illustrating results of a lightning test waveformof the TVS assembly;

FIG. 10 is a graph 900 illustrating results of a DC test of the TVSassembly; and

FIG. 11 is a graph 1000 illustrating results of the DC test shown inFIG. 9 of the TVS assembly.

DETAILED DESCRIPTION

The following detailed description illustrates embodiments of the systemby way of example and not by way of limitation. It is contemplated thatthe systems and methods have general application to electronic componentmanufacturing and packaging in power electronics, signal electronics,and electromagnetic interference (EMI) protection in industrial,commercial, and residential applications.

As used herein, an element or step recited in the singular and precededwith the word “a” or “an” should be understood as not excluding pluralelements or steps, unless such exclusion is explicitly recited.Furthermore, references to “one embodiment” of the present invention arenot intended to be interpreted as excluding the existence of additionalembodiments that also incorporate the recited features.

Embodiments of the present disclosure demonstrate a semiconductor basedTVS device that operates reliably at 300° C. In one embodiment, thedevice is fabricated from silicon carbide (SiC). In other embodiments,the devices are fabricated from other wide band gap materials such as,but not limited to, gallium nitride (GaN), diamond, aluminum nitride(AlN), boron nitride (BN), and combinations thereof. The wide band gapsemiconductor TVS device is reliably operable up to approximately 500°C., however, other components, such as, the TVS packaging may be morelimiting in the example embodiments. The TVS is a clamping device,suppressing approximately all over-voltages above its breakdown voltage.The TVS device typically comprises three SiC layers (N-P-N). In otherembodiments, the three layers comprise P-N-P layers. In an N-P-N typedevice, when the device is subjected to a potential across the two Nlayers, a depletion layer is formed (mostly) in the P layer because itsdoping is much lower compared to the two N layers. For example, one tofive orders of magnitude lower, or one-tenth to one ten-thousandth ofthe dopant concentration of the N layers. For a further example, if thedoping concentration in the N layers is approximately 10¹⁸/cm³, thedoping concentration in the P layers would be approximately 10¹⁵/cm³. Asthe voltage across the device is increased, the depletion region extendsall across the P layer and touches the N layer on the other side. Thisleads to a condition known as “punch-through” and a large amount ofcurrent begins flowing in the device. The device is able to maintainthis condition with minimal change in the voltage across it. A similarexplanation describes the operation when the polarity of the layers ischanged to P-N-P.

The package, in one example, is designed to have a low inductance andcapacitance to provide fast electrical response and to have a thermalcapacitance to manage thermal pulses. The low inductance and capacitanceis achieved by using short conduction paths from the die to thetermination which is bonded to the circuit. Glass or ceramicencapsulation may be used to protect the die from contamination in theenvironment and provide improved electrical insulation across thedevice. A borosilicate glass encapsulation has been found to have lowleakage current in testing up to 600° C. The termination material isselected to be compatible with ceramic-to-metal sealing and withglass-to-metal sealing, respectively. The termination material mayinclude but is not limited to tungsten, molybdenum, or Kovar®. The dieis bonded on both sides to respective terminations using for example, athermocompression bond, transient liquid phase solder bond, diffusionbond, or alloyed layer. In one embodiment, a gold thermocompression bondprovides a lower thermal resistance path and does not oxidize in hightemperature. Gold also has a large plastic range to provide a low stressinterface especially at high temperatures.

The TVS device facilitates preventing sensitive electronics coupled inparallel to the TVS device from being subjected to voltage spikes causedby, for example, lightning strikes and being damaged. In variousembodiments, more than one TVS device may be connected in a TVS assemblycomprising parallel, series, and/or series parallel configurations ofTVS devices to permit enhanced electrical protective features of the TVSassembly, for example, greater voltage or current capabilities. The SiCdevice in a high temperature package enables its deployment inenvironments with relatively high ambient temperatures, for example,greater than approximately 150° C. Moreover, the SiC device providesultra-rigid clamping. Although described herein as being suitable foruse in high temperature applications, the wide band gap materials arealso well suited for applications where the temperature is notrelatively high, for example, at room temperature.

FIG. 1 is a schematic block diagram of an architecture of a power andcommunication distribution system 100 in accordance with an exemplaryembodiment of the present invention. In the exemplary embodiment,distribution system 100 includes a power supply distribution bus 102 anda communications channel 104. Power supply distribution bus 102distributes electrical power to a plurality of electronics units 106located about an engine 110, in the exemplary embodiment. In theexemplary embodiment, engine 110 is a gas turbine engine comprising afan 112 and a core engine 114. In various other embodiments, engine 110may be another piece of machinery, such as, but not limited to, apiston-driven internal combustion engine, a compressor, a generator, anda pump. In the exemplary embodiment, plurality of electronics units 106include electronics units (EU) 116 and 118 illustrated as being mountedin a relatively cool environment proximate fan 112 of, for example, agas turbine engine (GTE) 110. Distribution system 100 also includes hightemperature electronics units (HT-EU) 120, 122, and 124. Each of HT-EUs120, 122, and 124 are illustrated as being mounted on core engine 114 ofgas turbine engine 110, which is a relatively hot environmentallocation. For example, a temperature in a vicinity of a core housing 114may be greater than approximately 150.0° Celsius (C) to approximately300.0° C.

EU 116 receives power from a power supply 126. The received power ismanaged for distribution within distribution system 100 by EU 116. Themanaged power is transmitted to various respective loads including EUs118, HT-EUs 120, 122 and 124 through power bus power supply distributionbus 102. Similarly, communications among the various electronic units istransmitted over communications channel 104.

During operation, electromagnetic interference and/or lighting strikesto the aircraft may induce large transient voltages spikes onto buses102 and/or 104. Such large voltage spikes, if not remediated, may causedamage to electrical and electronic components coupled to the busesincluding EUs 116, 118, and HT-EUs 120, 122, and 124. To avoid suchdamage, transient voltage suppressors may be used in series and/orparallel with selected components and/or circuits within components tofacilitate reducing and/or eliminating such spikes. One method clampsthe voltage on the bus to a predetermined level.

FIG. 2 is a schematic block diagram of an exemplary one of EUs 116, 118,and HT-EUs 120, 122, and 124 in accordance with an exemplary embodimentof the present system. In the exemplary embodiment, HT-EU 120, forexample, includes a processor 202, a memory 204 communicatively coupledto processor 202, a ROM memory 206, an input section 208, alsocommunicatively coupled to processor 202, a drive module 210, and anoutput module 212. HT-EU 120 also includes a communications module 214communicatively coupled to communications bus 104 and processor 202.HT-EU 120 further includes a power module 216 electrically coupled topower supply distribution bus 102 and configured to distribute power atvarious voltages throughout HT-EU 120. Being coupled to respectivebuses, communications module 214 and power module 216 are susceptible toEMI and/or lightning induced spikes. To prevent such interference andspikes from reaching communications module 214 and power module 216 anddownstream components, one or more transient voltage suppression (TVS)assemblies 218 and 220 are coupled between the respective buses andcommunications module 214 and power module 216.

FIGS. 3A-3C are schematic block diagrams of various configurations ofvoltage suppression protection available using TVS assembly 218 inaccordance with an exemplary embodiment of the present invention. In theembodiment of FIG. 3A, TVS assembly 218 comprises two transient voltagesuppressors in a series configuration. In the embodiment of FIG. 3B, TVSassembly 218 comprises two transient voltage suppressors in a seriesconfiguration in parallel with a third transient voltage suppressor. Inthe embodiment of FIG. 3C, TVS assembly 218 comprises two transientvoltage suppressors in a parallel configuration in series with a thirdtransient voltage suppressor. Various other combinations of individualtransient voltage suppressors maybe assembled to provide sufficientcurrent carrying capacity and a predetermined voltage performance formany different applications.

FIG. 4 is a side elevation view of a semiconductor die 302 portion of atransient voltage suppression (TVS) assembly 218 or 220 (shown in FIG.2) in accordance with an exemplary embodiment of the present system. Inthe exemplary embodiment, die 302 includes a mesa structure that isformed of a substrate 304 of for example, silicon carbide having an n+type conductivity and an epitaxially grown n+ type conductivity layer306, an epitaxially grown p− layer 308 coupled in electrical contactwith layer 306, and an epitaxially grown n+ layer 312 coupled inelectrical contact with p− layer 308. In the exemplary embodiment, P−layer 308 is relatively lightly doped relative to the n+ layers 306 and308. A uniform doping concentration of substrate 304 and layers 306,308, and 312 improves a uniformity of the electric field distribution inthe depletion region, thereby improving the breakdown voltagecharacteristic. Moreover, the mesa structure has a beveled sidewallangled approximately five degrees to approximately eighty degrees withrespect to an interface between adjacent contacting layers to reduce themaximum electric field profile at a surface of the die. A firstelectrical contact 310 is coupled in electrical contact with substrate304. A second electrical contact 314 is coupled in electrical contactwith epitaxially grown n+ layer 312. Semiconductor die 302 portion of atransient voltage suppression (TVS) assembly 218 or 220 operates using“punch-through,” or also known as, “reach-through” physics such that asthe voltage across die 302 is increased, a depletion region extends allacross P− layer 308 and touches n+ layers 306 and 312. This leads to acondition known as “punch-through” and large amounts of current are ableto flow through die 302. Die 302 is able to maintain this condition withminimal change in the voltage across it.

In various embodiments, TVS assembly 218 is sized and formed to ensure amaximum electric field internal to the semiconductor material of die 302is maintained less than two megavolts per centimeter. Additionally, TVSassembly 218 is configured to maintain an increase in blocking voltageof less than 5% for current in a range of less than approximately 1.0nanoamp to approximately 1.0 milliamp. As used herein, blocking voltagerefers to the highest voltage at which TVS assembly 218 does not conductor is still in an “off” state. Moreover, TVS assembly 218 is configuredto maintain an electrical leakage current of less than approximately 1.0microamp up to approximately the punch-through voltage of TVS assembly218 at room temperature and less than 1.0 microamp up to approximatelythe punch-through voltage at operating temperatures of up to 225°Celsius.

In various embodiments, TVS assembly 218 is configured to exhibit punchthrough characteristics between approximately 5.0 volts to approximately75.0 volts. In various other embodiments, TVS assembly 218 is configuredto exhibit punch through characteristics between approximately 75.0volts to approximately 200.0 volts. In still other embodiments, isconfigured to exhibit punch through characteristics greater thanapproximately 200 volts.

FIG. 5 is a side elevation view of semiconductor die 302 portion of atransient voltage suppression (TVS) assembly 218 or 220 (shown in FIG.2) in accordance with another embodiment of the present system. In theexemplary embodiment, die 302 includes a first frusto-conical structure402 and a second substantially cylindrical structure 404. Firstfrusto-conical structure 402 is formed of epitaxially grown n+ typeconductivity layer 306 and at least a portion of epitaxially grown p−layer 308. Cylindrical structure 404 is formed of at least a portion ofepitaxially grown p− layer 308 and epitaxially grown n+ layer 312. Inthe exemplary embodiment, p− layer 308 is relatively lightly dopedrelative to n+ layers 306 and 312. Uniform doping concentration ofsubstrate 304 and layers 306, 308, and 312 improves a uniformity of theelectric field distribution in the depletion region, thereby improvingthe breakdown voltage characteristic. A first electrical contact 310 iscoupled in electrical contact with substrate 304. A second electricalcontact 314 is coupled in electrical contact with epitaxially grown n+layer 312.

FIG. 6 is a side elevation view of semiconductor die 302 portion of atransient voltage suppression (TVS) assembly 218 or 220 (shown in FIG.2) in accordance with another embodiment of the present system. In theexemplary embodiment, die 302 includes a first frusto-conical structure602 and a second frusto-conical structure 604. First frusto-conicalstructure 602 is formed of epitaxially grown n+ type conductivity layer306 and at least a portion of epitaxially grown p− layer 308. Secondfrusto-conical structure 604 is formed of at least a portion ofepitaxially grown p− layer 308 and epitaxially grown n+ layer 312. Inthe exemplary embodiment, p− layer 308 is relatively lightly dopedrelative to n+ layers 304, 306, and 312. Uniform doping concentration ofsubstrate 304 and layers 306, 308, and 312 improves a uniformity of theelectric field distribution in the depletion region, thereby improvingthe breakdown voltage characteristic. A first electrical contact 310 iscoupled in electrical contact with substrate 304. A second electricalcontact 314 is coupled in electrical contact with epitaxially grown n+layer 312.

FIG. 7 is a side view of transient voltage suppression (TVS) assembly218 (shown in FIG. 2) in accordance with an exemplary embodiment of thepresent invention. In the exemplary embodiment, first and secondelectrical contacts 310 and 314 each includes a diffusion bonded oralloyed layer 702 and 704 and a respective header pin 406 and 408. Invarious embodiments, layers 702 and 704 are formed of copper (Cu), gold(Au), aluminum (Al), platinum (Pt) and combinations thereof. In otherembodiments, layers 702 and 704 may be formed of other materials,combinations or alloys. In various embodiments, first and secondelectrical contacts 310 and 314 are coupled to die 302 using layers 702and 704 using, for example, but not limited to, a thermocompressionbond, a transient liquid phase solder bond, a diffusion bond, or analloyed layer. Surface mount contacts 410 and 412 are coupled inelectrical contact with first and second electrical contacts 310 and314, typically to header pins 406 and 408 respectively. A glassencapsulation 414 at least partially surrounds die 302 and first andsecond electrical contacts 310 and 314. In various embodiments, glassencapsulation 414 includes borosilicate glass or an alumina ceramic.Header pins 406 and 408 are formed from a material selected to have acoefficient of thermal expansion that substantially matches acoefficient of thermal expansion of glass encapsulation 414. Suchmaterials may include at least one of tungsten, molybdenum, aniron-nickel-cobalt, low expansion alloy, sometimes referred to as Kovar®and a combination thereof. Kovar® alloy is a vacuum melted,iron-nickel-cobalt, low or controlled expansion alloy whose chemicalcomposition is controlled within narrow limits to assure precise uniformthermal expansion properties. In the exemplary embodiment, header pins406 and 408 are formed from a material comprising approximately 29%nickel (Ni), 17% cobalt (Co) and the remaining balance is substantiallyiron (Fe).

FIG. 8 is another view of transient voltage suppression (TVS) assembly218 (shown in FIG. 2) in accordance with an exemplary embodiment of thepresent system. In the exemplary embodiment, header pins 406 and 408 areformed having flanges 502 and 504 configured to mate with glassencapsulation 414 and to receive, for example, a solder connection toelectrically couple TVS assembly 218 to a circuit.

FIG. 9 is a graph 800 illustrating a lightning test waveform of TVSassembly 218. In the exemplary embodiment, graph 800 includes an x-axis802 graduated in units of time and a y-axis 804 graduated in units ofvoltage and current. A trace 806 represents a voltage imposed on TVSassembly 218, the peak of which points to the clamping voltage of TVSassembly 218. In the exemplary embodiment, it is approximately 100.0Volts. A trace 808 represents a current flowing through TVS assembly218, which is approximately 134 Amperes.

FIG. 10 is a graph 900 illustrating a DC test. In the exemplaryembodiment, graph 900 includes an x-axis 902 graduated in units ofvoltage and a y-axis 904 graduated in units of current using alogarithmic scale. A trace 906 represents a response of TVS assembly 218when subjected to a voltage across first and second electrical contacts310 and 312 and a corresponding current is measured. The DC test isperformed with TVS assembly 218 at approximately 200° Celsius todetermine a high temp capability of TVS assembly 218. In the exemplaryembodiment, TVS assembly 218 turns on at approximately 65.0 Volts wheretrace 906 goes flat. At voltages less than 65.0 Volts TVS assembly 218is in an “off” condition. The current flowing when TVS assembly 218 isoff is the leakage current. It can be seen that the leakage currentvalues through TVS assembly 218 are extremely small, for example, in thepico-ampere range) when TVS assembly 218 is off at high temperatureindicating low leakage currents.

FIG. 11 is a graph 1000 illustrating a DC test of TVS 218. In theexemplary embodiment, graph 1000 includes an x-axis 1002 graduated inunits of voltage and a y-axis 1004 graduated in units of current using alinear scale. A trace 1006 represents a response of TVS assembly 218when subjected to a voltage across first and second electrical contacts310 and 312 and a corresponding current is measured. The DC test isperformed with TVS assembly 218 at approximately 200° Celsius todetermine a high temp capability of TVS assembly 218. In the exemplaryembodiment, TVS assembly 218 turns on at approximately 65.0 Volts wheretrace 906 breaks sharply.

The above-described embodiments of a method and system of transientvoltage suppression provides a cost-effective and reliable means forreducing and/or eliminating voltage spikes induced into electricalsystems such as from EMI and/or lightning strikes. More specifically,the methods and systems described herein facilitate operation ofelectronic equipment subject to relatively high environmentaltemperatures. In addition, the above-described methods and systemsfacilitate operating electronic components in high density housingswithout additional cooling support. As a result, the methods and systemsdescribed herein facilitate operating vehicles, such as aircraft in acost-effective and reliable manner.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

The invention claimed is:
 1. A transient voltage suppressor (TVS)assembly comprising: a semiconductor die in a mesa structure comprising:a substrate comprising a layer of a first wide band gap semiconductorhaving a conductivity of a first polarity; a second layer of the firstor a second wide band gap semiconductor having a conductivity of asecond polarity coupled in electrical contact with said substrate, thesecond polarity being different than the first polarity; and a thirdlayer of the first, the second, or a third wide band gap semiconductorhaving a conductivity of the first polarity coupled in electricalcontact with said second layer, wherein said second and third layers atleast partially define a beveled sidewall forming an angle ofapproximately five degrees to approximately eighty degrees with respectto an interface between adjacent contacting layers, where said layerhaving a conductivity of the second polarity is lightly doped relativeto the layers having a conductivity of the first polarity; a firstelectrode coupled in electrical contact with said substrate; and asecond electrode coupled in electrical contact with said third layer,where when a voltage greater than a predetermined magnitude is appliedacross the first and second electrodes, the TVS assembly operates in apunch-though mode that permits a relatively large amount of current toflow through the TVS assembly.
 2. A TVS assembly in accordance withclaim 1, wherein said layers of semiconductor are formed by at least oneof epitaxial growth, diffusion, and ion implantation.
 3. A TVS assemblyin accordance with claim 1, wherein the voltage is applied at least oneof unidirectionally and bidirectionally across the first and secondelectrodes.
 4. A TVS assembly in accordance with claim 1, furthercomprising a glass or ceramic encapsulation at least partiallysurrounding said die and said first and second electrodes.
 5. A TVSassembly in accordance with claim 1, wherein said layer having aconductivity of a first polarity comprises an n+ type conductivity layerand said layer having a conductivity of a second polarity comprises a p−type conductivity layer.
 6. A TVS assembly in accordance with claim 1,wherein said layer having a conductivity of a first polarity comprises ap+ type conductivity layer and said having a conductivity of a secondpolarity comprises an n− type conductivity layer.
 7. A TVS assembly inaccordance with claim 1, wherein said substrate and said layers compriseat least one of silicon carbide (SiC), gallium nitride (GaN), diamond,aluminum nitride (AlN), boron nitride (BN), and combinations thereof. 8.A TVS assembly in accordance with claim 1, wherein for a layer having aconductivity of a second polarity comprising SiC, the concentration ofdopant is approximately one to five orders of magnitude less than theconcentration of dopant of the layer having a conductivity of a firstpolarity.
 9. A TVS assembly in accordance with claim 1, furthercomprising surface mount contacts coupled in electrical contact withsaid first and said second electrodes.
 10. A TVS assembly in accordancewith claim 1, further comprising a diffusion bonded or alloyed contactlayer positioned between each of said first and said second electrodesand said die.
 11. A TVS assembly in accordance with claim 10, whereinsaid diffusion bonded or alloyed contact layer comprises gold copper(Cu), gold (Au), aluminum (Al), platinum (Pt) and combinations thereof.12. A TVS assembly in accordance with claim 1, further comprising aglass encapsulation at least partially surrounding said die and saidfirst and second electrodes, wherein said first and said secondelectrodes comprise a coefficient of thermal expansion thatsubstantially matches a coefficient of thermal expansion of said glassencapsulation.
 13. A TVS assembly in accordance with claim 1, whereinsaid first and said second electrodes comprise at least one of tungsten,molybdenum, an iron-nickel-cobalt, low expansion alloy, titanium,nickel, gold and a combination thereof.
 14. A TVS assembly in accordancewith claim 1, further comprising a glass encapsulation at leastpartially surrounding said die and said first and second electrodes,wherein said glass encapsulation comprises at least one of aborosilicate glass and an alumina ceramic.
 15. A TVS assembly inaccordance with claim 1, wherein a maximum electric field internal tothe semiconductor material of less than two megavolts per centimeter ismaintained.
 16. A TVS assembly in accordance with claim 1, configured tomaintain an increase in clamping voltage of less than 30% at the peakvalue of current.
 17. A TVS assembly in accordance with claim 1,configured to maintain an electrical leakage current of less thanapproximately 1.0 microamp up to approximately the punch-through voltageof the assembly at room temperature.
 18. A TVS assembly in accordancewith claim 1, configured to exhibit punch through characteristicsbetween approximately 5.0 volts to approximately 75.0 volts.
 19. A TVSassembly in accordance with claim 1, configured to exhibit punch throughcharacteristics between approximately 75.0 volts to approximately 200.0volts.
 20. A TVS assembly in accordance with claim 1, configured toexhibit punch through characteristics greater than approximately 200volts.
 21. A TVS assembly in accordance with claim 1, further comprisinga beveled sidewall to reduce the maximum electric field profile at asurface of the die.
 22. A transient voltage suppressor (TVS) assemblycomprising: a semiconductor die in a mesa structure comprising: asubstrate comprising a layer of a first wide band gap semiconductorhaving a conductivity of a first polarity; a second layer of the firstor a second wide band gap semiconductor having a conductivity of asecond polarity coupled in electrical contact with said substrate, thesecond polarity being different than the first polarity; and a thirdlayer of the first, the second, or a third wide band gap semiconductorhaving a conductivity of the first polarity coupled in electricalcontact with said second layer, where said layer having a conductivityof the second polarity is lightly doped relative to the layers having aconductivity of the first polarity; a first electrode coupled inelectrical contact with said substrate; a second electrode coupled inelectrical contact with said third layer, where when a voltage greaterthan a predetermined magnitude is applied across the first and secondelectrodes, the TVS assembly operates in a punch-though mode thatpermits a relatively large amount of current to flow through the TVSassembly, wherein for a layer having a conductivity of a second polaritycomprising SiC, the concentration of dopant is approximately oneone-thousandth the concentration of dopant of the layer having aconductivity of a first polarity.
 23. A transient voltage suppressor(TVS) assembly comprising: a semiconductor die in a mesa structurecomprising: a substrate comprising a layer of a first wide band gapsemiconductor having a conductivity of a first polarity; a second layerof the first or a second wide band gap semiconductor having aconductivity of a second polarity coupled in electrical contact withsaid substrate, the second polarity being different than the firstpolarity; and a third layer of the first, the second, or a third wideband gap semiconductor having a conductivity of the first polaritycoupled in electrical contact with said second layer, where said layerhaving a conductivity of the second polarity is lightly doped relativeto the layers having a conductivity of the first polarity; a firstelectrode coupled in electrical contact with said substrate; a secondelectrode coupled in electrical contact with said third layer, wherewhen a voltage greater than a predetermined magnitude is applied acrossthe first and second electrodes, the TVS assembly operates in apunch-though mode and is configured to maintain an electrical leakagecurrent of less than 1.0 microamp up to approximately the punch-throughvoltage at operating temperatures of up to 225 degrees Celsius.